The present application is based on Japanese Patent Application Nos. 11-154995 and 2000-161793, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical disc capable of reading and writing data, and more particularly to an optical disc on which digital data including video data, still picture data and audio data are recorded. Moreover, the present invention relates to an apparatus and method of recording and reproducing data therefor.
2. Related Art
There is a DVD-RAM which is of phase change type and has a storage capacity of 4 GB or more as an optical disc capable of storing, reading and writing digital data including video and audio data.
Examples of the video digital data which can be recorded on the DVD-RAM are applied with a coding standard of an MPEG method. The MPEG method uses compression to code the video data at a variable bit rate (VBR).
The DVD-RAM is utilized as a home video recorder by compressing and recording video data by the MPEG method.
On the other hand, a home audio recorder for recording audio digital data, such as music, on the DVD-RAM is currently being developed.
Examples of recording methods of audio digital data which can be recorded on the DVD-RAM include LPCM (linear PCM), an audio compression standard 3 (AC 3) and a meridian lossless packing (MLP).
The LPCM is a non-compressive coding mode to be used in a CD, and typically codes audio information with 16 bit quantization. The DVD-RAM can record, for approximately nine hours, the audio data which are quantized at a sampling rate of 44.1 Khz in the LPCM. Although the LPCM is non-compressive and thus has an advantage that high tone quality can be obtained, it has a disadvantage that a rate of reading from the disc is high and a large recording capacity is required for the disc.
The AC3 compresses to code audio information at a constant bit rate (CBR). Since the AC3 serves to compress and code the audio information, it has an advantage that the rate of reading from the disc can be reduced and a other hand, the AC3 system has a disadvantage that the information is deteriorated during the compression, resulting in low tone quality than that in the linear pulse code modulation (LPCM).
The MLP system losslessly compresses and codes audio information at a variable bit rate (VBR). The lossless compression is a coding mode in which the tone quality is not deteriorated due to the compression. In deteriorating, the rate of reading from the disc is higher than that of the AC3 and can be more reduced than that of the LPCM.
In order to utilize the DVD-RAM as the home audio recorder, a data format and an apparatus capable of efficiently recording music information on a disc through the LPCM, the AC3 and the MLP and having high operability for a user when recording, editing and reproducing data are required as a data format of the optical disc and an apparatus thereof.
More specifically, the following three items are required for the data structure of the data format:
(1) To have path information in which a playback sequence having a combination of audio data having a constant bit rate (CBR) such as the LPCM and the AC3 and audio data having a variable bit rate (VBR) such as the MLP. This allows the user to reproduce, through the home audio recorder, various audio data in different coding modes which the user obtained from various data obtaining channels, without the user recognizing a difference in the coding mode.
(2) To have time map information for indirectly providing to a recording position on the disc of the audio data with reference to a time stamp. This can allow for easy modification of the information about the recording position of the audio data and a rapid editing work also in the home audio recorder having low hard performance when the recording position of the audio data on the disc is changed during an editing operation.
(3) To reduce the data size of the time map information in (2). This allows the time map information to be loaded into a memory in the home audio recorder on which a small capacity memory is mounted.
The present invention has been made to solve the above mentioned problems and has an object to provide an optical disc capable of-reducing the data size of time map information and an apparatus and method of recording and reproducing data for the optical disc.
In order to solve the above-mentioned problems, an recording medium for storing at least one audio object constant bit rate coding mode and management information for managing reproduction of the audio object, and has the following configuration.
In the optical disc, the audio object comprises a plurality of units each having a predetermined playback duration, each unit has the same playback duration except for the last one of all the units comprised in the audio object.
The management information includes path information which defines at least one reproducing interval, coding mode information indicative of coding mode of each audio object, and map information provided for each audio object. The map information converts the time stamp information specifying the reproducing interval of the audio object into an address on the optical disc storing the unit of the audio object to be reproduced at the time indicated by the time stamp information.
The map information comprises information about a data size of the unit. The information about the data size of the unit includes information about a data size of each unit when the coding mode of the corresponding audio object is the variable bit rate coding mode, or only information about a data size of a last one of the units included in the audio object and information about a data size of one of residual units except for the last unit when the coding mode of the corresponding audio object is the constant bit rate coding mode.
The map information may further comprise information about the playback duration of the unit. The information about the playback duration can include only playback duration information for a last one of the residual units except for the last unit. The information about the playback duration can included only playback duration information for one of the residual units except for the last unit.
The map information may comprise two table structures. The first table structure is referred when the coding mode of the corresponding audio object is the variable bit rate coding mode. The first table structure has information about a data size of the unit for each unit as the information about the data size of the unit. The second table structure is referred when the coding mode of the corresponding audio object is the constant bit coding mode. The second table structure has, as information about a data size of a unit, only information about a data size of a last one of the units included in the audio object and information about a data size of one of the residual units except for the last unit.
The variable bit rate coding mode may include at least one of AAC and MLP. The constant bit rate coding mode may include at least one of linear PCM and AC-3.
A data recording apparatus according to the above described optical disc; The apparatus comprises: a section for inputting audio data to be recorded and then deciding whether a coding mode of the input audio data is the variable bit rate coding mode or the constant bit rate coding mode; a section for creating the map information of the first table when the coding mode is the variable bit rate coding mode as a result of the decision, or creating the map information of the second table when the coding mode is the constant bit rate coding mode; and a section for recording the created map information in the optical disc together with the input audio object.
A data reproducing apparatus according to the invention is an apparatus for reproducing an audio object from the above described optical disc. The apparatus comprises: a section for specifying an audio object to be reproduced; a section for deciding whether a coding mode of the specified audio data is a variable bit rate coding mode or a constant bit rate coding mode; and a section for the unit comprised in the audio object to be reproduced from the map information with the selected table structure, obtaining a start address on the optical disc of the object reading and reproducing the audio object from the start address thus obtained.
In the data reproducing apparatus, the section for selecting a table structure can obtain the start address by the following method. When the decided coding mode is the variable bit rate coding mode, the method may comprise referring to the map information with the first table structure to obtain the data size for each unit, summing the data size thus obtained, and adding an offset address value of the audio object to be reproduced to the summed value. When the decided coding mode is the constant bit rate coding mode, the method may comprise referring to the map information with the second table structure to obtain the data size for one of the residual units, multiplying the obtained data size by the number of the units comprised in the audio object to be reproduced, and adding an offset address value of the audio object to be reproduced to the multiplied value.
A data recording method according to the audio data to be recorded and then deciding whether a coding mode of the input audio data is the variable bit rate coding mode or the constant bit rate coding mode; creating the map information of the first table when the coding mode is the variable bit rate coding mode as a result of the decision, or creating the map information of the second table when the coding mode is the constant bit rate coding mode; and recording the created map information in the optical disc together with the input audio object.
A data reproducing method according to the invention is a method for reproducing an audio object from the above described optical disc. The method comprises: specifying an audio object to be reproduced; deciding whether a coding mode of the specified audio data is a variable bit rate coding mode or a constant bit rate coding mode; and selecting a table structure of the map information in accordance with the decided coding mode, reading a size of the unit comprised in the audio object to be reproduced from the map information with the selected table structure, obtaining a start address on the optical disc of the object to be reproduced from the read size of the unit, and reading and reproducing the audio object from the start address thus obtained.
According to the present invention, by utilizing the fact that the playback duration of the object unit is constant, the playback duration of all the units are not recorded but the reproducing duration is recorded for only the first and last units in each object. Moreover, when the audio data are coded in a constant bit rate coding mode, utilizing the fact that the size of the unit in a pack is constant, the sizes of all the units are not recorded but the sizes are recorded for the first and last units in each object. Thus, the recording format of the time map position on the disc of the audio data with the time stamp is implemented for both of the constant bit rate coding mode and the variable bit rate coding mode. In the case of the variable bit rate coding mode, size of the time map information per recording time can be compressed to a half or less. In the case of the constant bit rate, the time map can be constructed with a constant size irrespective of the recording time. Consequently, the memory residence of the time map information can be carried out also in the home audio recorder having a small mounted memory.